GNFAC Avalanche Advisory for Thu Mar 12, 2009

The Bridger, Gallatin and Madison Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City and the Washburn Range:

I rode into the Lionhead area outside West Yellowstone yesterday. I saw two large avalanches that likely ran on a layer of facets two feet under the surface. Sure enough, in my stability tests I got this layer to fracture. Besides these two slides I saw no other activity in spite of the many miles ridden. But I’m not easily fooled. I’m betting there are some slopes on the brink of sliding, just waiting for an unlucky skier or rider to trigger them. Winds loaded most alpine slopes and skiers were able to trigger small wind slabs in the last two days. One person wrote that they would get slabs to break two to three feet deep and 40 feet wide from cornice drops.

Deeper in the snowpack are facets near the ground straining to hold up the winters snow. Yesterday I dug a seven foot snow pit to find these. I was in this exact location a week ago, but the snow was now three feet deeper. I carefully isolated a column, stemmed across the pit, and did a compression test. It broke clean 16 inches off the ground on 27 taps. Not good. Facets on the ground should never be trusted. Check out photos of recent avalanches and a video of my snow pit on our website.

Photos: http://www.mtavalanche.com/photos/photos.php

Video: http://www.youtube.com/watch?v=pGZmmPnTROQ

From last Wednesday through Monday morning the mountains got hit with two to three feet of snow and southwest winds. Clear skies made it easy to find avalanches that released this weekend. No mountain range was spared and some of the slides propagated for long distances. But what’s a bit surprising is that many slopes did nothing—they were strong enough to hold the load even though several buckled under the weight. We are now left with some slopes poised to avalanche in need of a little extra stress to tip the balance—like a snowmobiler or skier. As every day passes without new snow the probability of triggering a slide lessens, but the consequences of one are still ugly. The snowpack structure is weak and has the potential to avalanche. The situation we’re in now has similarities to the deadly weekend of January 17th: great snow, good riding/sliding and stability on many slopes, but a real possibility to trigger an avalanche. Because the weak layers are not uniform, the avalanche danger varies from slope to slope; more so than normal. In the next few days, snowmobile and ski tracks will start to mark up the hills. You may be tempted, especially in the warm sunshine, to assume that the snowpack is friendly, stable and inviting. You would be wrong. Consequently, the avalanche danger today is rated CONSIDERABLE on all wind-loaded slopes and MODERATE elsewhere.

UPCOMING EVENTS

Make plans to attend the 28th Annual Pinhead Classic Telemark Festival this Saturday, March 14th, at Bridger Bowl. This year’s theme is “The Olympics” with events for all ages and all abilities. Prizes are awarded for everything but the fastest time and all proceeds benefit the Friends of the Avalanche Center. A registration fee of $30 gets you a ½ -day rate lift ticket, t-shirt, commemorative pint glass, multiple laps on the dual slalom course, numerous prizes and awards, and dinner, dancing, unlimited beverages, and live music at the Emerson that evening. Visit www.pinheadclassic.com for more information.

Karl Birkeland will issue the next advisory tomorrow morning at 7:30 a.m. If you get out in the backcountry give us a call or send us an email with your observations. You can reach us at 587-6984 or at mtavalanche@gmail.com.